1. Technical Field
The present invention relates to a mirror adjustment method which adjusts the slants of at least two mirrors which are provided in a high output laser oscillator which is used for cutting, welding, and otherwise working a workpiece and a mirror adjustment system which performs such a method.
2. Description of the Related Art
In general, the output of a laser oscillator falls due to fouling and degradation of the inside mirrors which are provided at a resonator of a laser oscillator. For this reason, the inside mirrors have to be periodically detached from the resonator to be washed or replaced. Further, the inside mirrors are reattached to the resonator, then the inside mirrors are adjusted in slants to adjust the optical axis of the resonator.
The optical axis of the resonator of a conventional laser oscillator is adjusted in the following way. First, two mirrors are selected from the plurality of inside mirrors of the resonator. Note that, it is assumed that these inside mirrors are attached to a stage which is provided with two adjusting parts which make the inside mirrors slant in two perpendicularly intersecting directions.
FIG. 11 is a view which shows the relationship between the slant of a first mirror among the two mirrors and the laser output in the prior art. An adjusting part of the first mirror is used to set the slant of the first mirror to a certain value in one direction among two perpendicularly intersecting directions and an adjusting part of a second mirror is adjusted in the same direction so that the laser output becomes a maximum value. Such an operation is performed a plurality of times so as to obtain a relationship M between the slant of the first mirror and the maximum value of the laser output at that time which is shown in FIG. 11. The relationship M which is shown in FIG. 11 is asymmetric at the left and right. The reason is that when there are a large number of inside mirrors of the resonator, there are inside mirrors which remain unadjusted and these affect the relationship M.
In FIG. 11, a point M0 is the maximum value of the laser output as a whole. Further, a line parallel to the abscissa is drawn at a location smaller than the value of the point M0 by exactly a predetermined ratio. This predetermined ratio is, for example, 10% to 30%. Then, the two intersecting points of this line and relationship M are set as M1 and M2. Then, the adjusting part of the first mirror is used to set a center point MC which is shown by the arrow between the intersecting points M1 and M2 as the slant of the first mirror. In this case, the passing area through which the laser light passes between the two mirrors which are adjusted becomes the largest.
Further, the adjusting part of the second mirror is used to adjust the slant of the second mirror so that the maximum value of the laser output is obtained. After this, a similar operation is performed in another direction as well. Furthermore, when the number of inside mirrors of the resonator is large, other inside mirrors are combined and successively adjusted. By this, it is possible to increase the passing area of passage through the discharge tube as a whole to obtain laser light with less interference and less output loss.
Japanese Patent Publication No. 5-37050A similarly discloses to successively make one inside mirror among a pair of inside mirrors slant while adjusting the other inside mirror so that the laser output becomes a maximum value.
FIG. 12 is another view which shows the relationship between the slant of the first mirror and the laser output in the prior art. In FIG. 12, first, the slant of the first mirror is adjusted from the line L1 which is parallel to the ordinate to the right direction, but the maximum value of the laser output is not obtained so the slant of the first mirror is adjusted from the line L1 to the left direction. In such a case, the number of adjustment operations increases and as a result there is the problem that the work time becomes longer. In particular, when the peak part in the relationship M is relatively flat, the number of adjustment operations has to be increased and similarly the work time becomes extremely long.
Further, in the configuration of Japanese Patent Publication No. 5-37050A, at each detection point, the amount of change with respect to the average value of the laser output at the previous detection point is used as the basis to adjust the inside mirrors. By performing such processing, the number of adjustment operations until convergence becomes extremely great and shortening the work time is difficult. Furthermore, when the peak part is relatively flat, the work time becomes extremely long.
The present invention was made in consideration of such a situation and has as its object the provision of a mirror adjusting method which enables the work time to be greatly shortened and a mirror adjusting system which performs such a method.